Train line communication and control stem

ABSTRACT

An asymetrical, astable multivibrator, at the control location for a multiple unit train, transmits a control signal having a selected duty cycle characteristic over a single train line channel. The duty cycle percentage is selectively varied by a transistorized switching bank which connects different resistors into the RC timing circuit for one-half of the multivibrator element, the other half having a fixed timing circuit. These switching transistors are selectively controlled by the train operator in accordance with the desired train operating mode. The transmitted control signal is received on each car and converted into an average voltage whose level varies with percent duty cycle. On each car, this average voltage is compared, in a transistorized comparator element, with a reference voltage preset in accordance with the desired operating mode of that car within the overall train operation. When the average voltage is less than the reference voltage, a controller on that car is actuated to control the car function. With different reference voltages preset on the several cars, sequential activation of the car control functions may be obtained.

limited Mates Patent [451 Mar. 2%, 1972 Grundy [54] TRAlN LlNECOMMUNICATION AND @ONTROL STEM [72] inventor: Reed 1111. Grundy,Murrysville, Pa.

[73] Assignee: Westinghouse Air Brake Company, Swissvale, Pa.

[22] Filed: Apr. 14, 1970 [21] Appl. No.: 28,378

[52] 1.1.8. Cl. ..105/61, 317/140, 340/167 A [51] lnt.Cl ..B60l15/08[58] Field of Search ..325/38, 64; 343/225; 307/271;

[56] References Cited UNITED STATES PATENTS 2,930,888 3/1960 Crawford etal. ..317/139 X 2,462,134 2/1949 Scully ..340/167 A X 2,515,968 7/1950Shanklin.. ..340/167 A 2,724,745 11/1955 Brewer ...340/172 X PrimaryExaminer-Arthur L. La Point Assistant Examiner-George H. LibmanAttorney-H. A. Williamson, A. G. Williamson, Jr. and J. B. Sotak [57]ABSTRACT An asymetrical, astable multivibrator, at the control locationfor a multiple unit train, transmits a control signal having a selectedduty cycle characteristic over a single train line channel. The dutycycle percentage is selectively varied by a transistorized switchingbank which connects different resistors into the RC timing circuit forone-half of the multivibrator element, the other half having a fixedtiming circuit. These switching transistors are selectively controlledby the train operator in accordance with the desired train operatingmode. The transmitted control signal is received on each car andconverted into an average voltage whose level varies with percent dutycycle. On each car, this average voltage is compared, in atransistorized comparator element, with a reference voltage preset inaccordance with the desired operating mode of that car within theoverall train operation. When the average voltage is less than thereference voltage, a controller on that car is actuated to control thecar function. With different reference voltages preset on the severalcars, sequential activation of the car control functions may beobtained.

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SHEET 2 0F 2 [mar/W 0 Ry Reed f1. Granary TRAIN LINE COMMUNICATION ANDCONTROL STEM My invention relates to a train line communication and/orcontrol system. More particularly, this invention relates to acommunication system for transmitting control functions or indicationsbetween an operator's location and the several cars ofa multi-car,self-propelled train.

in the basic or prior art arrangement for communicating between cars ofmulti-car train, for example, in rapid transit systems, direct currentenergy is applied at one end ofa physical train line wire to cause someaction or reaction at the other end of the wire, or even at severallocations one on each car of the train. These actions or reactions maybe the resulting control or movement ofa controllable function on thetrain. In the former system, therefore, the control was either on or offonly. For example, one typical controllable function comprises thepropulsion motor or motors, which were either turned on or turned off onall cars. Another typical controllable function is the brake pressurewhich could either be turned on or off at some selected levelsimultaneously on each car of the train. In other words, such controlfunctions were transmitted from the operators location simultaneously tosimilar apparatus on each of the several cars. Although such train linesare multiwire cables, many of the wires must be assigned fortransmitting indications or controls pertaining to the operation of thecar doors, the positioning of the train signs, the turning on or off ofcar lights, and the transmission ofindications or measurements of thebraking air pressure available. The more modern and sophisticatedpropulsion and brake control concepts which have been developed toprovide a smoother and more comfortable ride, as well as more efficientoperation, require additional control functions. It is impracticable orat least quite expensive to provide additional train line wires. At thesame time, it is not possible to eliminate any of the direct on or offcontrol functions for other items of equipment as above enumerated, thatis, doors and train signs. Therefore, a need exists for some arrangementwhich will provide additional communication channels over an existingtrain line cable so that a sufficient number of control functions orsignals may be transmitted to properly control the newer and moresophisticated propulsion and braking systems.

Accordingly, one object of this invention is an improved train linecommunication system.

Another object is a novel arrangement providing additional control orcommunication channels over existing train line cable wires.

A further object of this invention is communication apparatus thattransmits several distinct functions over a single train line wire.

Still another object is a control function transmission atrangement forindividually controlling functions on several cars ofa train over asingle wire in the train line cable.

It is also an object of this invention to provide a communication systemfor transmitting a plurality of functions over a single channel in theform of signals having a distinct duty cycle characteristic for eachfunction to be transmitted.

A further object of the invention is an arrangement for transmittingsimilar functions successively to several cars of a train over a singletrain line wire using signals with selected duty cycle characteristicshaving successive increments as functions are transmitted to additionalcars.

Other objects, features, and advantages of this invention will becomeapparent from the following specification when taken in connection withthe appended claims and accompanying drawings.

In practicing my invention, 1 provide a transistorized, asymmetrical,astable multivibrator at the function transmission location which isassociated with the operators control panel for the train. The timing ofthe first condition of this multivibrator, i.e., when a first transistorconducts, is controlled by a fixed series resistance-capacitance timingcircuit. However, the timing for the second condition of themultivibrator, i.e., other transistor conducting, is variable and iscontrolled by a fixed capacitor and a selected one of several timingresistors. The selected resistor is switched into the timing controlcircuit by an associated transistor, one being provided for each of thefunction selections. The conditioning of this associated transistor toconnect the timing circuit resistor with the corresponding capacitor iscontrolled by the operator's selection of a particular operating modefor the motors and/or brakes of the train which he is controlling. Thismode selection is here supplemental to the normal control stand withwhich the train is provided and which is incapable of actuating thisparticular communication system. The output signal of the multivibratoris supplied to the preselected train line wire upon which issuperimposed this multichannel communication system of the invention.The resulting signals applied to the train line are a series of on"pulses which are transmitted over the selected train line wire. Each on"pulse, which corresponds to the first condition of the multivibrator, isof fixed duration. However, each corresponding or alternating off' pulseis varied in duration in accordance with the operators control functionselection. This results in a function control signal characteristicrepresented by the variable duty cycle of the on pulses. Thus the actualsignal characteristic by which the control function is transmitted, thatis, the duty cycle characteristic, is a function of the operatorscontrol lever selection.

At each function location, the receiver apparatus is connected so as tobe interposed in the normal direct connection between the train line andthe function controller at that location. Specifically, the functioncontroller is shown as a propulsionbrake control unit for each car ofthe train. The transmitted function control signal is received by asingle transistor registry stage of the receiver. This stage is sodesigned as to produce an average voltage signal which varies as theduty cycle characteristics of the incoming signal changes. Atwotransistor comparator arrangement compares this average voltage levelwith a reference voltage level preset for the particular location. Inthis specific illustration, the reference voltage is preset inaccordance with the desired operating mode for that particular car, inother words, how that car is to operate within the overall operation ofthe train during its movement along the track. The reference voltagesetting thus establishes a control limit for the location receiver andmore specifically, a control limit for operation of the comparator orlevel detector element. Depending in a predetermined manner upon thecomparison between the average and the reference voltage levels, atransistorized amplifier element functions to actuate, on or off, thefunction controller winding for that particular location, that is, asspecifically shown, to control the propulsion and brake function forthat car. Each car of the train thus functions similarly in receivingthe control signals, although not simultaneously, in accordance with thevarious preset reference voltage levels on each car and the duty cyclecharacteristic of the signal transmitted from the control location.

I shall now describe in greater detail the arrangement embodying myinvention, referring to the accompanying drawings in which:

FIG. 1 is a schematic block diagram of an arrangement embodying theinvention as applied to a typical four car train of a rapid transitsystem.

FIG. 2 illustrates control transmitter apparatus embodying features ofthe invention and usable in the arrangement shown in FIG. 1.

FIG. 3 illustrates receiver apparatus embodying features of my inventionand also usable in the FIG. 1 arrangement as indicated therein.

In each of the figures of the drawings, where applicable, similarreference characters refer to similar parts of the apparatus. Also inFIGS. 2 and 3, a direct current source of energy, suitable for theoperation of the illustrated transistor circuits, is assumed.Preferably, this source of energy is the same as that applied for theoperation of the other conventional carcarried apparatus. Forconvenience, this direct current supply is illustrated only by thesymbol B+, designating a connection to the positive terminal, and aconventional ground symbol designating a connection to the oppositeterminal of the source. As will be explained later, it is possiblethrough the specific arrangement of the circuitry of my invention to usethe regular car-carried direct current source of energy even though itsactual voltage level may vary slightly from time to time.

Referring now to FIG. 1, the schematic block diagram illustrates a trainline communication and control arrangement embodying my invention asapplied to control the propulsionbraking apparatus function on each caron a typical four car train unit which, for example, may be used in arapid transit system. A control location for the train operator is shownon each end of the train which is a conventional arrangement to alloweither direction operation of the train. Obviously, only one suchcontrol location is in use at any one time. As will also be understoodby those familiar with such transit systems, each car ofthe train mayhave a control location so that it may be used as a lead car but, forsimplicity, only two such locations are shown in the train unitillustrated. Each control location has a control stand illustrated bythe conventional block which is typically a manually operated contactorcontroller. When such control is used, all of the brake and propulsionunits on the train, that is, on all cars, operate in unison. Suchcontrols are transmitted over train line wires as on" and off" signalsto the various function controls on each car. My invention adds to thisarrangement a control transmitter, also shown by a conventional block sodesignated, at each control location. This apparatus provides for aselective control operable by the train operator, the details of whichare illustrated in FIG. 2 as referenced on the block diagram. Thearrangement superimposes this selective control apparatus on a singletrain line channel designated in FIG. 1 by the reference 35. As will beunderstood, and become obvious later, this channel is actually a singlewire of the train line cable and the usual ground return circuit path.As will also become apparent, only one of these control transmitterswill be active at any one time, that is, the one at the location atwhich the train operator is at that time stationed.

At each controlled apparatus or function location, receiver apparatus isinterposed between the function controller and the train line 35carrying the selective signals. It is to be noted that, in the prior artarrangements, the function control apparatus is normally connecteddirectly to the train line or lines so that no selective operation carby car is possible unless sufficient train line wires can be providedfrom the control stand locations. In this present arrangement, areceiver apparatus responds in a preset manner in accordance withoperational limit characteristics preselected for each car location. Inother words, the signal transmitted from the control location isreceived by each receiver unit in a selected characteristic signal formand is translated and compared with a preset operational limit for thatlocation. If the received signal properly meets certain selectedrequirements, it is further translated into a function control signaland actuates the associated function in the desired manner. Thesecontrol functions are progressively actuated from car to car as desiredby system operation and in accordance with preset control limitsestablished when the train is made up. The details of the receiverapparatus are shown in FIG. 3, as referenced in FIG. 1, and will beshortly discussed.

Referring now to FIG. 2, shown are the detailed circuits for the controltransmitter unit illustrated by the conventional block in FIG. 1. Thebasic element of this transmitter is an asymmetrical, astable orfree-running, multivibrator element comprising transistors Q5 and Q6 andthe associated connections. The operation of multivibrator elements ofthis general type are sufficiently well known that a detaileddescription is unnecessary herein and a brief description is includedonly for an understanding of the specific operation provided in thepresent arrangement. The timing period for a first condition of themultivibrator, in which transistor O5 is conducting, is fixed by theresistance-capacitor timing circuit including resistor R12 and capacitorC2. This specific circuit, of course, extends from the B+ tenninalthrough the cited resistor and capacitor and the collector-emitter pathof transistor O5 to the ground terminal. Since this is a fixed timingcircuit, it is obvious that the off or nonconducting time period fortransistor Q6 is always of the same duration. The timing for the secondcondition of the multivibrator, in which transistor O6 is conducting,is, however, variable. This timing is established by whichever one ofthe resistors R5 through R8 is connected in a series RC circuit withcapacitor C1. The actual connection is controlled by the switchingtransistors Q1 through Q4, inclusive. For example, if transistor O1 isbiased to a conducting condition, resistor R5 is connected in seriescircuit with capacitor C1, the circuit extending from terminal 8+through resistor R10, the emitter-collector path of transistor Q1,resistor R5, capacitor C1, and the collector-emitter path of transistor06 to ground terminal.

The switching transistors 01, Q2, Q3, and Q4 are controlled by a controlselector switch CSK. This switch, or operating lever, is locatedadjacent to the control stand at a control location for the train and isoperable by the operator to exercise a more selective control of thespecific apparatus with which it is related. As shown in FIG. 1, thisapparatus, for example, may be the propulsion and brake controller unitson each car. Switch CSK is positioned in its OFF position when thatparticular control location is not in use, that is, is not in the leadcar of the train. The four numbered positions designate the type or modeof train operation which results when the switch is so positioned. Thesenumbered positions may also be considered as designating more simply thenumber of cars in a four car train on which the corresponding controlledapparatus is selectively turned on or off." The operation of the switchCSK to each numbered position specifically connects the base of thecorrespondingly numbered transistor 01 to Q4 to the ground terminal sothat that transistor and, of the four, that transistor only becomesconducting. When any one of these transistors is in its conductingcondition, the resistor connected to the collector terminal is connectedin series circuit with capacitor C1, as previously described, to providea particular selected timing period for the second condition of themultivibrator element. By a proper selection of the values of resistorsR5 to R8 in designing the system, a progressive sequence of operatingtimes for transistor Q5 may be obtained as switch CSK is moved to selectthe various operating modes 1 to 4, respectively.

The output of the multivibrator element, from the collector terminal oftransistor Q6, is applied to the base of transistor Q7 which isconnected in an emitter follower arrangment. The output of this latterarrangement, at the emitter terminal of transistor O7, is supplied asthe transmitted signal to the train line 35, which is a singlecommunication circuit path as illustrated in FIG. 1. Transistor Q7 isobviously conducting when transistor O6 is in its nonconductingcondition and the output supplied to channel 35 is thus a 8+ potentialpulse when transistor O6 is turned off." Therefore the positive pulsesin the signal on train line 35 are of equal duration. Conversely, theOFF" or ground potential pulses vary in time duration in accordance withthe operating time of transistor Q5. Thus the positive code pulses onchannel 35 have a duty cycle characteristic, that is, a percent ON timein accordance with the position of selector switch CSK. It is to benoted that the frequency of the ON pulses is not the importantcharacteristic of the transmitted signal, but only the total time thepositive or ON pulse is present within a preset time period, e.g., acomplete cycle of operation comprising an ON time and the following OFFtime.

I shall refer now to FIG. 3 for the circuits for the receiver unitsupplied on each car of the train. Signals supplied by the transmitterof FIG. 2 are received over train line 35 at resistor R16 at the left ofthe circuits shown. These signals are applied to the base terminal oftransistor Q8. This transistor registers and converts the incomingsignal pulses into a steady state direct current signal which isproportional to the voltage on terminal B+ and the percent duty cyclecharacteristic of the received signal. This steady state direct currentis also defined as an average value signal which varies in level inaccordance with variations in the duty cycle characteristic. Thisaverage voltage signal appears at the common junction of resistors R18,R19, and capacitor C3. Obviously this average value voltage signal, asdetermined by the duty cycle characteristic, is applied to the base oftransistor Q9.

Transistors Q9, Q10, and Q11 form a level detector or comparatorelement, with transistor 010 connected only to provide a constantcurrent source for transistors 09 and Q11. The signal applied to thebase of transistor Q11 is a reference voltage obtained from terminal B+selectively through resistors R26, R27, R28, or R29 with the voltagedivider arrangement completed through resistor R30. Capacitor C4 isconnected as a bypass to drain any ripple voltage appearing at the B+terminal. The operating mode selector switch OMSK is preset, when thetrain is originally assembled, to provide the desired individualoperation of that car in the overall train operation. For example,switch OMSK may be set at the numbered position corresponding to theposition of that car in the train. In other words, on the first car ofthe train, switch OMSK would be set at position 1 and correspondingly,for the second, third, and fourth cars in the four car train shown inFIG. 1, at positions 2, 3, and 4, respectively. Other methods ofselection of the car operating modes are possible as different operatingconditions for the train are desired. It is assumed for the remainingdescription that a sequential selection is used in the train in FIG. 1,that is, the switch position number corresponds to the car number withinthe train.

It is to be noted that the average voltage signal applied to the base oftransistor Q9 and the reference voltage signal at the base of transistorQ11 are both derived from the B+ terminal of the corresponding car sincethe complete receiver unit is provided on each car of the train. Anychange in the level of 8+ will affect each applied signal by the sameratio of change. Therefore, voltage variations in the direct currentsource on a particular car, that is, changes in the voltage level at B+terminal, will not affect the comparison of the signals applied to theopposite sides of the comparator unit. This ratio elimination of theeffects of voltage changes also eliminates the need for a separate,constant voltage power source on each car, that is, separate from theusual power supply provided for other car apparatus. Provision of such aseparate source is inconvenient and inefficient since it requiresadditional and redundant equipment.

The comparator element is preferably so designed that, when the averagevoltage signal level is less than that of the reference voltage,transistor Q9 becomes conducting and transistor Q11 is turned off."Conversely, when the average voltage signal is greater than the level ofthe reference voltage preset for that car, transistor Q11 only conducts.In the FIG. 3 receiver circuits, the remaining transistors Q12, Q13, andQ14 form an amplifier elements to control or drive the functioncontroller apparatus represented by the winding L. This amplifierelement is conventional circuitry in the art and its operation isunderstandable without specific description herein. The winding L, ofcourse, represents the control function being controlled by thecommunication system, specifically shown in HO. 1 as being thepropulsion and brake unit apparatus. It is to be understood thatsupplemental controls may be applied to select between varioussubelements of this overall function control unit in a conventionalmanner over other wires of the train line. Such arrangements are notinvolved in the invention described herein and thus are not shown.

Briefly considering the amplifier element, it is obvious that whentransistor Q11 is nonconducting, transistor Q12 is also in itsnonconducting condition. In this situation transistor Q13 is triggered,so that both it and transistor 014 are in their conducting condition.Winding L is then energized to actuate the control function to a desiredcondition or position. If transistor Q11 is conducting, that is, thereference voltage is less than the average voltage signal in thecomparator element, transistor Q12 is also biased to its on condition.With this latter condition conducting, transistors Q13 and 014 arebiased to their off or nonconducting condition. Winding L is thendeenergized and the control function is conversely actuated or releasedaccording to its characteristics.

Considering now a specific operational situation, it is assumed that itis desired to provide the train operator with the facility to have thecars of the four car train, FIG. 1, respond in a sequential manner totransmitted control functions regarding the propulsion and brake unitapparatus on each car. This operational selectively is provided in lieuof the more conventional all on or all Oh type of operation. A typicalselection of the resistors R5 through R8 will then provide, as aspecific example, a duty cycle characteristic for the transmitted signalranging between an percent duty cycle when resistor R5 is connected andreducing to a 50 percent duty cycle characteristic when resistor R8 isin service. Each intervening resistor provides a correspondingintermediate characteristic signal level. Said in another manner, whenlever CSK occupies its position 1, transistor 01 conducts. The RC timingcharacteristic for the circuit through resistor R5 and capacitor C1 isrelatively short so that the off-time or nonconducting period fortransistor O5 is also short. Conversely, transistor Q6 ontime isrelatively short so that the off time of transistor O7 is also short. Asignal having a potential of B+ is then transmitted 80 percent of thetime over train line 35, the remaining 20 percent of each cycle being aground or OFF potential pulse. At the other extreme position of switchCSK, that is, position 4, transistor O4 is conducting. Resistor R8 is soselected that the timing characteristic of the circuit includingresistor R8 and capacitor C1 is equal to the timing characteristic ofthe circuit including resistor R12 and capacitor C2. It will be obviousthat under these conditions the B+ signal pulse on line 35, through theoperation of transistor Q7 under these conditions, is equal to the OFFor ground potential pulse so that the duty cycle is 50 percent.Obviously, the circuit parameters can be so designed that the lowestduty cycle is less than 50 percent if desirable in system operation, orrequired to obtain specific operating situations. Specifically, whenswitch CSK is positioned at points 2 or 3, the duty cycle will be at aselected characteristic between the assumed 80 percent and 50 percentcharacteristics of the extreme positions, such as, by way of specificexamples, 70 percent and 60 percent, respectively.

The same characteristic signal is, of course, applied over train line 35to the base of transistor Q8 in the receiver on each car of the train.This actuates conduction of transistor Q8 during the positive pulseportion of each cycle so that the operating condition of transistor Q8has the same duty cycle characteristic. If it is further assumed thatresistor R18 is equal in value to resistor R19 in the circuit throughand including the collector-emitter path of transistor Q8, then theaverage voltage signal level, at the junction of these two resistors andcapacitor C3, will be one-half of the 13+ terminal voltage level timesthe duty cycle percentage. Specifically, for example, if resistor R5controls the transmitter multivibrator element, the average voltagesignal at the base of transistor O9 is then 40 percent of the B+ voltagelevel. This result is obtained by taking 80 percent of one-half of theB+ level in the voltage divider circuit. Also specifically, whenresistor R8 controls the multivibrator characteristic output, theaverage voltage signal at transistor Q9 is at a level of 25 percent ofthe B+ terminal voltage level.

With the specific assumptions used above to describe examples oftransmitted characteristic signals, the reference voltage level at thebase of transistor Q11, with switch OMSK in position 1, must be greaterthan 40 percent of B+ voltage. In other words, R26 on each car must beso selected as to divide the voltage potential between B+ and groundterminals, when the divider includes resistors R26 and R30, that thevoltage potential at the common junction of these two resistors isslightly more than 40 percent of the total available from the B+terminal. Under the same assumptions, resistor R29 on each receiver mustbe so selected that, when this resistor is selected by positioningswitch OSMK to its number 4 position, the reference voltage is greaterthan percent of the B+ terminal voltage potential but less than this B+terminal voltage multiplied by one-half the duty cycle characteristicestablished by resistor R7 at the transmitter location. For example, ifa 60 percent duty cycle results from the selection of R7, then thereference voltage established by the selection of resistor R29 must beless than percent but more than 25 percent of 8+. The values of theother resistors R27 and R28 must be selected in a similar manner so thatwhen either of these resistors is used in the voltage divider circuit toestablish the operating characteristic, the reference voltage will beproperly established between upper and lower limits set by theassociated duty cycle characteristics of the transmitted controlsignals. Such values may be calculated, if desired, by reference to theabove description but are not specifically defined herein.

It is now further assumed that, for the cars of the train of FIG. 1, theswitches OSMK are set in sequence from the leading end at positions 1,2, 3, and 4, respectively, on the correspondingly numbered cars. Thenthe train operator, by positioning switch CSK at its number 1 position,will actuate only the control function winding L on the first car. inother words, with the average voltage at the base of transistor Q9 oneach car being at percent of 8+ voltage, the average voltage will begreater than the reference voltage or operating control limit on all butthe first car of the train. On this first car, the average voltage levelis less than the reference voltage level since switch OMSK is positionedto include resistor R26 in the voltage divider network. As previouslyexplained, this results in a reference voltage signal greater than 40percent of 8+ terminal voltage. Under these conditions, the amplifierelement including transistors O12, Q13, and Q14 operates to energizewinding L. Only when control selector switch CSK is in its position 4,so that the duty cycle characteristic is established at percent, is theaverage voltage less than the reference voltage on each car. Under theseconditions, the average voltage is at 25 percent ofthe B+ terminallevel. In this condition, the controller winding L on each car isenergized. Obviously, the circuit parameters may be selected to giveother values of the transmitted characteristic signals and the referencevoltage levels so that additional cars may be included in the train orother operating conditions may be provided for the operators selection.

The system of my invention thus provides an unique and effectivecommunication arrangement which adds capacity to a train linecommunication arrangement. The system provides for a transmission ofadditional control functions which allow smoother and more efficienttrain operation. The arrangement is also so designed that a specialpower supply on each car is avoided and the normal car power supply maybe used since the effect of variations in the B+ terminal voltage levelare, by the ratio arrangement, cancelled out in comparing the averageand the reference voltage signals on each car. An effective, efficient,and practical arrangement thus results and provides additionalcommunication and/or control channels over a fixed number oftrain linewires.

Although i have herein shown and described but a single form of thesystem embodying my invention, it is understood that changes andmodifications within the scope of the appended claims may be made in theillustrated arrangement without departing from the spirit and scope ofthe present invention.

Having thus described my invention, what I claim is:

l. A train line control system for transmitting control functions over asingle communication channel between two locations on a multi-car train,comprising in combination,

a. a multivibrator means for producing periodic pulses having a presetform and connected for transmitting said pulses through said train linechannel,

b. a selector means operable to select a desired one ofa plurality ofcontrol functions, I I c. said selector means controlling saidmultivibrator means for establishing a different duty cyclecharacteristic for said periodic pulses for each possible controlfunction selection,

d. averaging means connected for receiving said periodic pulses andresponsive thereto for registering an average signal in accordance withthe characteristic duty cycle of the received pulses,

e. a level detector having a preset operating characteristic andcontrolled by said averaging means for determining the relationshipbetween said averaged signal and the preset operating characteristic,and

. function control means controlled by said level detector for actuatingan associated control function when said averaged signal has apredetermined relationship to said operating characteristic.

2. A train line control system as defined in claim 1, furthercomprising,

a. an averaging means for each car of said train connected for receivingsaid periodic pulses and responsive thereto for registering the sameaveraged signal on each car for each different duty cyclecharacteristic,

b. a level detector associated with each averaging means, each leveldetector having a different preset operating characteristic andcontrolled by the associated averaging means for determining therelationship between the averaged signal and the corresponding operatingcharacteristic, and

c. a function control means controlled by each level detector foractuating the associated control function only when said predeterminedrelationship exists between the averaged signal supplied to, and theoperating characteristic of, the controlling level detector.

. A train line control system as defined in claim 2 in which,

a. said multivibrator means and said selector means are located at thecontrol station of said train,

b. each set of averaging means, level detector, and function controlmeans is located on a different car of said train,

c. the preset operating characteristics of the plurality of leveldetectors are ofsuccessively different levels, and

d. the duty cycle characteristic associated with each of said pluralityof control functions has a successively different value for successivelyactuating the control function on an additional car of said train assuccessive control functions are selected by said selector means.

. A train line control system as defined in claim 3 in which,

a. said multivibrator means is an asymmetrical astable transistorizedmultivibrator element having a fixed timing circuit for one transistor,

b. said selector means includes a transistor switching bank which variesthe timing circuit for the other transistor of said multivibratorelement to change the duty cycle characteristic of the pulsed output asdifferent control functions are selected,

c. each level detector is a two transistor comparator circuit with saidaveraged signal applied as an average voltage to the control terminal ofone transistor and said operating characteristic applied as a presetreference voltage to the control terminal of the other transistor,

d. each level detector being adjusted for actuating the correspondingfunction control means only when the averaged signal voltage is lessthan the reference voltage.

1. A train line control system for transmitting control functions over asingle communication channel between two locations on a multi-car train,comprising in combination, a. a multivibrator means for producingperiodic pulses having a preset form and connected for transmitting saidpulses through said train line channel, b. a selector means operable toselect a desired one of a plurality of control functions, c. saidselector means controlling said multivibrator means for establishing adifferent duty cycle characteristic for said periodic pulses for eachpossible control function selection, d. averaging means connected forreceiving said periodic pulses and responsive thereto for registering anaverage signal in accordance with the characteristic duty cycle of thereceived pulses, e. a level detector having a preset operatingcharacteristic and controlled by said averaging means for determiningthe relationship between said averaged signal and the preset operatingcharacteristic, and f. function control means controlled by said leveldetector for actuating an associated control function when said averagedsignal has a predetermined relationship to said operatingcharacteristic.
 2. A train line control system as defined in claim 1,further comprising, a. an averaging means for each car of said trainconnected for receiving said periodic pulses and responsive thereto forregistering the same averaged signal on each car for each different dutycycle characteristic, b. a level detector associated with each averagingmeans, each level detector having a different preset operatingcharacteristic and controlled by the associated averaging means fordetermining the relationship between the averaged signal and thecorresponding operating characteristic, and c. a function control meanscontrolled by each level detector for actuating the associated controlfunction only when said predetermined relationship exists between theaveraged signal supplied to, and the operating characteristic of, thecontrolling level detector.
 3. A train line control system as defined inclaim 2 in which, a. said multivibrator means and said selector meansare located at the control station of said train, b. each set ofaveraging means, level detector, and function control means is locatedon a different car of said train, c. the preset operatingcharacteristics of the plurality of level detectors are of successivelydifferent levels, and d. the duty cycle characteristic associated witheach of said plurality of control functions has a successively differentvalue for successively actuating the control function on an additionalcar of said train as successive control functions are selected by saidselector means.
 4. A train line control system as defined in claim 3 inwhich, a. said multivibrator means is an asymmetrical astabletransistorized multivibrator element having a fixed timing circuit forone transistor, b. said selector means includes a transistor switchingbank which varies the timing circuit for the other transistor of saidmultivibrator element to change the duty cycle characteristic of thepulsed output as different control functions are selected, c. each leveldetector is a two transistor comparator circuit with said averagedsignal applied as an average voltage to the control terminal of onetransistor and said operating characteristic applied as a presetreference voltage to the control terminal of the other transistor, d.each level detector beinG adjusted for actuating the correspondingfunction control means only when the averaged signal voltage is lessthan the reference voltage.